I don't think you'll find anything reliable online.
If your amulets are pre-BE 2516, the recourse would be to refer to the "canonical" 5 volumes of competition results (I forget the name of the competition, but it's a royally-sponsored one). Once you make a preliminary identification of a possible provenance, you'd refer to the specialist reference books for that particular phim/model to confirm the provenance.
Unfortunately, the 5 vol set is out of print and copies can cost a bomb. I hear a 2nd hand copy of Vol 5 is going for THB2,000 per copy in Bangkok.
Lek Watruak's sites, while informative, only scratch the surface of the hobby. His catalogue would probably account for less than 1% of the pre-war amulets that hobbyists show at competitions.
PS - BE 2516 is just a rough guestimate, based on my recollection of a competition entry of one amulet released that year.